An electrostatic chuck which attracts and holds a semiconductor substrate (e.g., silicon wafer) is used for various devices (e.g., ion implantation device, ion doping device, and plasma immersion device) utilized in a semiconductor production process. In the field of liquid crystal production, an electrostatic chuck which attracts and holds a glass substrate (i.e., insulating substrate) is used for a substrate bonding device utilized when sealing a liquid crystal between the insulating substrates, an ion doping device, and the like.
A device using an electrostatic chuck must reliably determine whether or not the electrostatic chuck holds a substrate in order to enable a continuous or automated production process. For example, ion implantation or the like cannot be performed if the substrate is not attracted to the electrostatic chuck. On the other hand, if the substrate cannot be removed from the electrostatic chuck, the substrate cannot be transferred to the subsequent step. It is important to check the presence or absence of the substrate for the production process using such a device in order to achieve mass production.
When using a bipolar electrostatic chuck which attracts a substrate due to the potential difference between two electrodes, a substrate detection device is generally used which detects whether or not the substrate is attracted to the electrostatic chuck by measuring the capacitance between the electrodes. For example, JP-A-7-7074 (Patent Document 1) discloses a method which detects a case where a substrate is absent, a case where a substrate is present but is not attracted, and a case where a substrate is attracted using a capacitance detection circuit connected between the electrodes of the electrostatic chuck. JP-A-2000-228440 (Patent Document 2) discloses a method in which a capacitance measurement device is provided between the electrodes of the electrostatic chuck, and the electrostatic chuck is moved vertically to accurately detect whether or not the electrostatic chuck sufficiently attracts and holds a substrate. A line of electric force produced from the electrodes of the electrostatic chuck generally reaches a substrate held by the electrostatic chuck. Therefore, when a substrate having a high dielectric constant (e.g., the relative dielectric constant of a silicon wafer is about 5.4) as compared with a vacuum is present, the capacitance between the electrodes increases. FIG. 5 schematically shows such a state. Since a line of electric force (partially indicated by a broken line in FIG. 5) produced between electrodes 10 and 11 reaches a substrate W, the capacitance between the electrodes differs depending on the presence or absence of the substrate W.
In recent years, along with an increase in demand for flat panel displays, the panel size of flat panel displays has been increased. For example, some liquid crystal mother glass substrates have dimensions larger than 2×2 m. In order to process such a large substrate, it is necessary to further increase the attraction force (holding force) of an electrostatic chuck. The inventors of the present invention have proposed an electrostatic chuck using an electrode sheet obtained by stacking two electrode layers in the depth direction of the electrode sheet through an inter-electrode insulating layer instead of disposing two electrodes side by side in a plane, differing from a known bipolar electrostatic chuck (see Patent Document 3). An electrostatic chuck which has a high dielectric strength and exhibits an attraction force sufficient for a large substrate can be obtained by stacking two electrode layers in the depth direction of the electrode sheet through an inter-electrode insulating layer.
When two electrode layers are stacked in the depth direction of the electrode sheet, the capacitance between the electrodes is mainly determined by the area over which the electrode layers disposed through the inter-electrode insulating layer are opposite to each other. FIG. 6 schematically shows such a state. Specifically, lines of electric force which occur between the electrodes are classified into a line of electric force which reaches the substrate W (indicated by a broken line I) and a line of electric force which occurs only between the electrodes (indicated by a broken line II). The line of electric force (II) mainly occurs. Therefore, when two electrode layers are stacked in the depth direction of the electrode sheet, the capacitance between the electrodes does not differ to a large extent depending on the presence or absence of the substrate. As a result, the presence or absence of the substrate may not be accurately detected using a substrate detection device utilizing the above-mentioned substrate detection method.    Patent Document 1: JP-A-7-7074    Patent Document 2: JP-A-2000-228440    Patent Document 3: WO 2005/091356